To compare the effects of verapamil and nifedipine on left ventricular (LV) systolic function and diastolic filling in pts with hypertrophic cardimyopathy, we assessed radionuclide angiograms in 11 pts during control and during oral therapy with each drug. Neither drug altered LV ejection fraction, at rest or during exercise. Verapamil, but not nifedipine, improved diastolic filling (increased peak LV filling rate and decreased time to peak filling rate) at rest. Both drugs improved diastolic filling during exercise, and the effects of verapamil and nifedipine were not different. These mechanisms may contribute to the clinical improvement of many pts during oral therapy with calcium channel blocking agents.